Iron oxide



Sept. 17, 1935, FREEMAN 2,015,053

IRON OXIDE Filed Sept. 16, 1932 lNVENTOR ,WQL F/ZLMM BY M Curl MATTORNEYS Patented s 11, 1935 IRON OXIDE Horace Freeman, Montreal,Quebec, Canada, assignor to Nichols Engineering 85 Research Corporationof Canada, Limited Application September 16, 1932, Serial No. 633,439 InCanada August 31, 1932 2 Claims.

This invention or discovery is comprised in a novel product, largelycomprising a magnetic ox de or oxides of iron in finely divided form.

The flotationprocess of concentrating copper and zinc from the mixedsulphide ores which are abundant in America, now makes available largequantities of a concentrate of iron pyrite, finely divided andcontaining about 50 per cent of sulphur.

In my United States patent application, Serial No. 433,471, filed March5, 1930, (corresponding to Canadian Patent No. 311,130 of May 5, 1931) asuitable apparatus and process are described for treating suchconcentrates by flash roasting to economically recover sulphur dioxidegas therefrom. I have discovered that when this process is properlycarried out, a resulting solid residue may be obtained, comprising aproduct having unusual prcperties rendering the same desirable for awide field of uses.

The accompanying figure of .the drawing comprises a copy of aphoto-micrograph illustrating a group of particles of said calclneproduct, which comprises the subject matter of this invention.

A process by which this product may be formed may be described asfollows. Of the pyrite now available for the economical manufacture ofthis product, I prefer flotation pyrite dried to less than 2 per cent or3 per cent moisture content and containing about 50 per cent of sulphuron the dry basis. I have determined, however, that the ordinary largelump pyrite containing somewhat 5s sulphur may also be quitesuccessfully used. Such material may be first fed by a regulated feedingdevice from a storage hopper into a ball mill which may serve as adrier, as a grinder, and also to bring the sulphide into suspension inthe air. In the case of lump pyrite, a fullcharge of balls is used inthe mill, but in the case of flotation material a very light charge ofballs is preferable, since it is necessary only to break up anyagglomeration. Warm air may be admitted into the mill to carry out thematerial brought into suspension, through a fan, and then into a primarycombustion chamber. In this chamber the temperature is preferablymaintained above 1100 C. in its middle zone, but the temperature of theburning particles is much higher than this and results in a very rapidand substantially complete removal of the sulphur from the particleswhich fuse while falling through the atmosphere of the chamber. If careis taken not to burn too much of the material per unit of time and perunit of volume in the chamber, no fluxing of the material on the wallsis experienced. In other words, to

avoid slag or crust formations in this chamber, preferably the chambershould be of ample size so that no substantial quantity of the fallingparticles contacts with the walls. For example, I have found that inorder to prevent slag or crust 5 formation, the amount of pyriteconsumed in the combustion chamber should not exceed two pounds percubic foot of combustion space per hour. Under these conditions, while athin crust may form from time to time on the walls, such crust iscontinually falling away and being renewed without causing anydifficulty in the operation of the process.

By regulating the feeding device and the speed of the fan or blower, therate of feed of ore into the chamber and the amount of velocity of airentering with the ore, may be regulated as desired. An outlet for thegases from the combustion chamber is preferably provided through one ormore of the walls near the top thereof. At the bottom of the chamber theside walls preferably are made to converge to an opening through whichthe solid particles drop on to a conveyor and through which asupplemental supply of air is also drawn up into the combustion chamber,this additional supplemental supply of air being drawn in by suctionmeans acting through the gas outlet. Such supplemental air supply ispreferably regulated so that the upwardly moving current of air in thechamber offsets the initial downward velocity of the ore particlesandpartially offsets the eflfect of gravity on the same, so that thedescent of the particles through the chamber is retarded.

In starting the process, the combustion chamher is suitably preheated.Then, after the proper temperatures have been created,the process may becontinued without use of extraneous fuel and three defined zones areestablished within the chamber. The upper or heating zone extends somedistance downwardly from the nozzle through which the ore is admitted.The atmosphere in this zone is usually largely sulphur dioxide andnitrogen rising from below. The sulphide particles in passing throughthis zone are heated to ignition and fusion temperature. If there isfree sulphur in the ore, some of this may be here volatilized andburned.

In the middle or primary combustion zone, the sulphide particles ignite,this being a zone of in-- tense combustion and complete fusion, in whichmost of the sulphur is burned to sulphur dioxide with the air introducedalong with the sulphide and with some of the air drawn in at the bottomof the combustion chamber. Possibly some of the enter'this bottom zone,they are individually vis-.

ible as a shower of brightly sparkling points of light and it'is.believed that in this zone most of the ironand the residual sulphur isburned. The intense heat of the individual particles indicated by thecondition of incandescence, is largely absorbed by'the particles at themoment of liberation, in maintaining the fused state of iron oxide,sothat the temperatureof the atmosphere in this zone is'lower than thetemperature of the individual particles. As the particles leave thisbottom zone, they are chilled and solidified by the incoming air andalso serve in some measure to preheat the air. The solid material whichpasses out counter-current to the incoming air at the bottom of thefurnace through the opening, constitutes the novel product of myinvention here involved.

The gases passing out at the top of the combustion chamber may befurther treated for the recovery and use of the sulphur dioxide and forthe utilization of the heat thereof. Suitable processes and apparatusfor such purpose are disclosed in the above mentioned patents. whichalso describe in some respects in further detail the apparatus andprocess above referred to.

The solid idue or caicine forming the subject matter of this inventionmay be described as fol lows. In the condition in which it leaves thecombustion chamber, this oxide material is in the form of relativelyfine, discrete, separated, fused, highly magnetic particles, many ofwhich appear as broken hollow shells. The material is of a grayish blackappearance and contains about 65 per cent of iron, largely combined asmagnetite. While it contains the gangue material ordinarily produced inflotation concentrate, it has been found that by magnetic separation,substantially all of such material may be eliminated. If this product isproperly produced, according to the above described process the sulphurcontent thereof may be kept below 0.2 per cent.

This product maybe used to advantagefor a variety of purposes. Forexample, it provides a high grade inn ore. free from phosphorus and lowin sulphur content, which may be sintered or briquetted, or may be usedas a raw material for sponge-iron production to be directly melted inelectric furnaces, without the usual cooling of the iron powder andmagnetic separation between the reducing kiln and the electric meltingfurnace. Thisproductmayalsobeusedasafrit or fiux in the manufacture ofbrick, such as magnesite brick. In view of the manner in which theproduct is formed, as-above described, the heavy but fine particles areoxidized and fused to a uniform degree. Furthermore, each of the smallparticles becomes cooled individually before leaving the roaster andlargely without contacting with other particles until aftersolidification has taken place. Accordingly, in its preferred form theproduct is neitherin the form of a sintered mass nor agglomerated. andneither are the fused particles in suchform asto render the productdusty and as compared with various finely divided iron oxide productsheretofore known. In the formation of a material by the process abovedescribed, any fine dust which might be obiectionable in the product iscarried away with the 5 outlet gases'from the combustion chamber so thatit does not fall with the desired product through the opening in thebottom of the furnace. Since,

despite the fused character of the particles, the

material is still of a finely divided and uniform 10 character, it maybe readily and uniformly mixed with other finely divided or granularmaterials whereby it may be used for a variety of purposes which wouldbe impossible or diflicult with a fused agglomerated mass of magneticiron oxide. The 15 finely divided character of the material alsofacilitates the magnetic separation of the same from the gangue materialor any crust materials falling from the walls of the combustion chamber.

The shell-like character of the product is believed to be due to thefact that as the sulphide particles enter the furnace, they rapidlyevolve elemental sulphur and in doing so, become puffed up, assuming theform of broken minute hollow balls. This feature of the process has theadvan- :3 tage that each particle thus presents a large surface foroxidation as it slowly falls within the uprising air current. In view ofthe method in which the product is thus formed, it will be apparent thatthe material of each particle is treat- 30 ed with uniformitysubstantially throughout.

It will be appreciated that the sulphide particles are maintained insuspension in the air within the furnace during the entire process ofoxidation and by regulating the velocities of the 35 two air supplies,the period of time during which the particles are held in suspension maybe made materially longer than would be normally occupied in thegravitation of the particles to the bottom of the chamber, and in thisway ample time is provided for thorough combustion.

If it should be desired to form the product for any special purposes ina somewhat agglomerated form, this may be readily done by using a com- Fbustion chamber of somewhat less height so that the particles are stillincandescent at the point where they fall through the opening at thebottom of the chamber.

While the product comprising. this invention and the process "andapparatus for forming the same have been described with mpect'to certainparticular preferred and satisfactory examples, it will be understood bythose skilled in the art after understanding the nature of the product,that various changes and modifications may be made without departingfrom the scope of the invention, and it is intended therefore in theappended claims to cover all such modifications.

What is claimed as new and desired to be secured by Letters Patent is:

1. Magnetic iron oxide in the form of fine individually oxidized andfused particles, individually solidified in the form of separate hollowshells.

2. Iron oxide, a substantial portion of which is 65 of the compositionof magnetite, in the form of fine individually oxidized and fusedparticles, individually solidified in the form of separate

